Grip reinforcing bar and method of producing same

ABSTRACT

A reinforcing bar with improved adherence for reinforced concrete component, consists of a metal profile section ( 1 ) in the form of a flattened strip of rectangular cross section with two opposite wide faces ( 10, 10 ′) on which longitudinally separated projecting anchoring portions are formed.

The invention has for object a reinforcing bar with improved adherencefor a reinforced concrete component, in particular a beam, a slab or acolumn, and also covers the reinforcing cages using such bars and themethods of producing same.

It is known that the principle of the reinforced concrete consists incombining the quality of compression strength of concrete with that oftensile strength of metal reinforcements. A reinforced concreteconstruction element indeed performs as a composite component in whichthe reinforcing bars and the concrete, which have close expansioncoefficients, are deformed in the same way under the applied stresses,at least up to a limit load.

In the case, for example, of a reinforced concrete component subjectedto flexion forces, it is usually considered, for the calculation of thereinforcements, that this component includes, on either side of aneutral axis, two portions subjected to respectively compression forcessupported by the concrete and tensile forces supported essentially bythe longitudinal reinforcing bars. It is hence determined by calculationthe cross-section that it is advisable to give to each bar in tension toresist to the forces applied, taking into account the distance betweenthe facing of the compressed portion and the centre of gravity of thebar.

Generally, the whole reinforcement of a reinforced concrete element hasthe form of a cage consisting in two webs of longitudinal bars,respectively active and passive, connected to each other by transversestirrups that allow the handling and positioning of the whole cage andthat, on the other hand, resist to the shearing stresses.

As the external forces that act upon a reinforced concrete element aregenerally applied to the concrete, it is the adherence link at the levelof the steel-concrete interface, i.e. the concrete sheath surroundingeach bar, which allows placing under load the reinforcements, necessaryfor normal functioning of the structure. The transfer capacity of theloads between the concrete and the reinforcing bar, thus, depends uponthe quality of this adherence link.

It is known that, when the tensile force applied in the portion undertension of a reinforced concrete component increases, it is firstlyobserved an almost linear phase during which the tensile force istransferred in each bar by the steel-concrete interface thatprogressively degrades up to appearance, in the concrete, of microcrackscaused by small displacements between the bar and the concrete thatsurrounds the latter. If the tensile forces continue to increase, thisfirst almost-linear phase is followed by a non-linear phase during whichthe microcracks localize into macrocracks, less numerous and larger,which form a “fishbone” network, with a loss of adherence and stiffnessof the interface.

These macrocracks allow the penetration of humidity and aggressiveagents in contact with the reinforcement. As they firstly appear on theside where the coating is less important, it is necessary to leave aminimal distance of coating between a reinforcing bar and thecorresponding facing of the component to avoid corrosion of the bar andbursting of the concrete. This distance of coating imposed by theRegulation may be, for example, of 30 mm.

A long time ago, it has already been proposed, in the documentFR-A-765,943, to improve the strength of a reinforced concrete beam byreplacing the round bars of circular cross-section commonly used asreinforcements by flat bars in the form of rectangular cross-sectionmetal strips, while keeping this imposed minimal distance.

Indeed, in such an arrangement, the width and the thickness of each flatbar may be chosen so as to have the cross-section usually determined bycalculation to resist to the forces applied. Such flat reinforcing barsare hence, with a same cross-section, equivalent to the round barsusually used but, for a same distance of coating, the axis of the flatbar is more distant from the centre of gravity of the beam than that ofthe round bar of same cross-section and the strength of the beam maythen be improved.

Likewise, for a same strength, the use of flat reinforcing bars allowsto reduce the whole thickness of the reinforcing cage and, hence, of theconcrete component, while keeping the same lever arm between the bars intension and the opposite facing.

However, to prevent the concrete from sliding with respect to the bar,it has been provided, in the document FR-A-765,943, to form, on one faceof the bar, a series of recesses made by rolling and each correspondingto a projecting boss on the other face. These bosses and cavities formedon the two wide faces, respectively, of the bar have a significantheight, of the same order as the thickness of the strip, so as torealize a perfect link between the bar and the concrete, whilepreventing any sliding one over the other.

However, to allow the formation of such bosses, these latter have to bespaced apart from each other by a distance of the same order as thewidth of the flat bar and hence exert on the coating concrete punctualstop forces, separated from each other, which, beyond a certain level oftension, may cause the appearance of more open macrocracks, with a riskof bursting of the concrete.

Such an arrangement hence allows no progressivity in the transmission ofthe forces between the bar and the concrete sheath, which remainperfectly cohesive up to a limit tensile force, beyond which the barrisk to brutally come away from the concrete.

Besides, the making of a series of bosses on one face and of cavities onthe other face provides the flat bar, in the central portion thereof,with a corrugated profile including, in the longitudinal direction, asuccession of thickness narrowings that constitute weakness pointsharmful to the tensile strength and liable to cause a rupture of the barfor a force that is much lower than the theoretically applicable limitforce. Moreover, the arrangements provided in this patent, published in1934, have never been applied in practice.

The invention has for object to solve such problems and to thereforeavoid the drawbacks of this prior technique while however benefitingfrom all the advantages offered by the use of flat bars with improvedadherence as reinforcements for reinforced concrete.

The present invention hence generally relates to the production of areinforcing bar with improved adherence for a reinforcing concretecomponent, consisting in a metal section extending in a longitudinaldirection, having the form of a flattened strip of substantiallyrectangular cross-section, with two opposite wide faces extendingbetween two lateral sides and including a plurality of projectinganchoring portions which are longitudinally separated from each otherand bearing on the concrete in a direction opposite to a tensile forceapplied to the bar.

According to the invention, each of the two wide faces of the strip isprovided with a series of anchoring portions in the form of elongatedlocks separated from each other by hollow portions in the form ofgrooves and extending transversally over the whole width of the strip,substantially up to the lateral sides thereof, and each of saidelongated locks extends in projection over a small height, not exceedinga quarter of the thickness of the strip, and has, in cross-section, asubstantially trapezoidal profile, with an embossed face of small widthwith respect to its length and two inclined flanks for connection withthe elongated bottom of the adjacent grooves that constitute, for eachlock, two inclined faces that bear, each in one direction, on thecoating concrete, said inclined faces each having an elongated shapeextending between the two sides of the strip, so as to distribute thebearing forces over all the width thereof.

Thanks to such arrangements, it becomes possible to ensure an excellentdistribution of the bearing forces over the whole rectangular perimeterof the bar, without risk of brittleness of the latter and with themaintaining, over its whole length, of a cross-section as constant aspossible, to resist in the best conditions to the tensile forcesapplied.

In a particularly advantageous manner, the elongated locks formed oneach face of the strip are spaced apart from each other by a constantpitch that do not exceed half the width of the strip and, preferably,comprised between one and three times the thickness of the strip.

Preferably, the locks formed on the two wide faces, respectively, of thestrip, are parallel to each other, and the locks formed on one face arelongitudinally shifted by a half pitch with respect to the locks of theopposite face, in such a manner that the bottom of each groove of afirst face is substantially opposite to a lock of the second face.

In a preferential embodiment, the elongated locks formed on the twofaces, respectively, of the strip, extend transversally in directionsinclined by a non-zero angle with respect to the longitudinal axis ofthe strip.

According to another preferential characteristic, the elongated locksformed on the two faces, respectively, of the strip, are symmetricallyinclined, in opposite directions, with respect to the longitudinal axis.

Advantageously, on each face of the strip, the angle 13 of inclinationof the locks with respect to the axis is comprised between 35° and 75°.

In a particular embodiment, the anchoring locks formed on each wide faceof the strip have the shape of imbricated V-shaped chevrons, with tworectilinear portions symmetrically inclined on either side of thelongitudinal axis of the strip.

In another embodiment, the anchoring locks have a corrugated shape,symmetrical with respect to the longitudinal axis of the strip.

According to another preferential characteristic, the locks formed oneach wide face of the strip extend up to a small distance from each ofthe lateral edges of the latter, so as to leave, along each of saidedges, a smooth flat of small width, of the order of 0.2 e, e being theaverage thickness of the strip.

Advantageously, on each of the two wide faces of the strip, the embossedfaces of the elongated locks and the bottoms of the grooves are locatedin two parallel planes, respectively, extending on either side of a meanplane in which are placed the two flats extending along the two lateraledges, respectively, of the strip.

Preferably, the two planes in which are located the embossed faces ofthe locks and the bottoms of the grooves, respectively, are spaced apartby a height h that can be from 0.08 e to 0.24 e, e being the averagethickness of the strip.

Besides, the connecting flanks between the embossed faces of the locksand the bottom of the corresponding grooves, which constitute, for eachlock, two elongated faces that bear, each in one direction, on theconcrete, are inclined by an angle of at least 45°, with respect to theembossed face of said lock.

The invention also covers a reinforcing cage for a reinforced concretecomponent, including two webs of reinforcing bars connected by stirrupsand extending at a small distance of coating from two spaced-apartfacings, respectively, of the component.

According to the invention, at least one of the two webs of the cageconsists in such flat bars with improved adherence and the stirrups arealso formed of flat metal strips, alternately welded on the embossedfaces of the elongated anchoring locks formed on each of the wide facesof said flat bars.

But the invention also covers a method of producing such reinforcingbars with improved adherence. According to the invention, it is firstlymade a metal bar in the form of a flattened strip with two opposite widefaces and centred on a longitudinal axis, then this flattened strip issubjected to a rolling pass between two cylinders rotating about axesparallel to each other and orthogonal to the longitudinal axis of thestrip, said cylinders being provided, over their periphery, withspaced-apart recesses for the formation, by rolling, of elongated locksseparated by parallel grooves, on each of the two wide faces of thestrip.

These two rolling cylinders are each provided, over their periphery,with an alternation of recesses and teeth intended to form the locks andthe grooves, respectively, on each of the wide faces of the strip andextending between two smooth portions of small width, for the formationof two flats along the two lateral sides of the strip.

Normally, these lock formation recesses are regularly spaced apart alongthe periphery of each of the rolling cylinders, so as to form locksspaced apart by a constant pitch. But, in some cases, the recesses maybe distributed along the periphery of each of the rolling cylinders insuch a way to vary periodically the spacing between the locks made oneach wide face of the strip.

But the invention will be better understood by the following detaileddescription of some preferential embodiments, given by way of simpleexamples and shown in the appended drawings.

FIG. 1 schematically shows, in perspective view, a reinforcing baraccording to the invention, provided with locks orthogonal to itslongitudinal axis.

FIG. 2 schematically shows, in two embodiments, the effect of a tensileforce applied to such a bar.

FIG. 3 is a partial perspective view of a reinforcing bar provided withlocks inclined with respect to its longitudinal axis.

FIG. 4 is a schematic sectional view of such a bar according to a planeorthogonal to its longitudinal axis.

FIG. 5 is a top view of a bar provided, on its two faces, with locksinclined in opposite directions.

FIG. 6 is a sectional view of a bar of FIG. 5 according to a planeorthogonal to its longitudinal axis.

FIG. 7 is a detail sectional view of this bar according to a planeparallel to its longitudinal axis.

FIG. 8 is a detail sectional view of a reinforcing cage usinglongitudinal bars according to the invention.

FIG. 9 shows, in top view, two alternative embodiments of a reinforcingbar according to the invention.

FIG. 10 schematically shows the steps of production of a reinforcingbar.

FIG. 11 is a detail sectional view of rolling cylinders according to theline I-I of FIG. 10.

FIG. 12 is a cross-sectional view of another embodiment of a flattenedbar.

In FIG. 1, which is a half detail, longitudinal sectional view, it hasbeen shown, in a perspective view, a first embodiment of a reinforcingbar according to the invention, consisting in a flat metal strip 1centred on a longitudinal axis x′ x and having a rectangularcross-section with two opposite, respectively upper 10 and lower 10′,wide faces extending between two lateral sides 11.

Each of the two wide faces 10, 10′ of the strip 1 is provided with aseries of regularly spaced apart, elongated projecting portions 2, 2′,separated from each other by hollow portions in the form of grooves 3,3′.

Each projecting portion 2, 2′ hence forms an elongated lock that has, incross-section with respect to its direction, a substantially trapezoidalprofile with an embossed face 21 and two inclined flanks 22, 23 ofconnection with the rectangular bottom 31 of two grooves 32, 33extending respectively on either side of the lock 2. These locks 2extend transversally over almost the whole width I of the strip 1,substantially up to the lateral sides 11 of the latter and arerelatively close to each other, the pitch c of spacing between twosuccessive locks being at most equal to half the width I of the strip.

For a reinforcing bar of reinforced concrete, the ratio of the nominalwidth to the nominal thickness is normally comprised between 4.5 and 6.Preferably, the spacing pitch of the locks will hence be comprisedbetween one and three times the thickness of the strip.

The so close-together locks 2, as well as the grooves 3 that borderthem, have hence an elongated rectangular shape, with an embossed face21 of very small width with respect to its length.

Such a reduced spacing pitch between the locks allows to form three orfour parallel locks over a strip length corresponding to the widththereof, whereas, in the prior arrangement of the document FR-A-765,943,the locks were spaced apart by a distance of the order of the stripwidth.

This multiplication of the number of locks hence allows, for equivalentbearing forces, to considerably reduce the height of the locks and,hence, the risk of fracturing of the coating concrete.

In practice, the height of the locks, i.e. the space between the levelof the embossed faces 21 and that of the bottom 31 of the grooves 3,shall not exceed the quarter of the thickness e of the strip and willpreferably be comprised between 0.08 e and 0.25 e.

Moreover, as the locks have a length substantially equal to the width ofthe strip, the connection flanks 22, 23 have also the shape of elongatedrectangles, of very small width with respect to the length thereof.

The so-constituted bearing faces hence allow, on the one hand, to reducethe individual stop forces applied by each lock on the coating concreteand, on the other hand, to distribute these forces over the whole widthof the strip.

In the embodiment illustrated in FIGS. 1 to 3, the elongated locks 2 aredirected perpendicular to the longitudinal axis x′ x of the strip 1 andare regularly spaced apart by the pitch c, whereas the locks 2′ of theopposite face 10′ are longitudinally shifted by a half-pitch. The bottom31′ of each groove 3′ of the lower face 10′ is hence located opposite tothe embossed face 21 of a lock 2 of the upper face 10.

As indicated above, in the prior technique described in the documentFR-A-765,943, it is made, in the central portion of one of the widefaces of the flat reinforcing bar, a series of cavities each determiningthe formation of a projecting boss on the other face. The cavities andthe bosses having a height of the same order than the thickness of thebar, it results therefrom a corrugated profile with a succession ofpoints of lesser strength.

On the other hand, in the invention, due to the fact that the locks 2′2′are formed on the two faces 10, 10′ of the strip and that they have avery small height, the thickness of the active portion resisting to thetensile forces remains of the same order than the nominal thickness ofthe reinforcing bar and is almost kept over the whole length thereof, inthe direction of application of the tensile force.

It is to be noted that, for more clarity, it has been given a maximalheight to the locks represented in FIGS. 2 and 3.

As schematically shown in FIG. 2, when the grooved flat bar 1 embeddedin the concrete is subjected to a tensile force T, the front inclinedflank 22 of each lock 2 exerts on the concrete, in the longitudinaltensile direction, bearing forces F, distributed over the whole lengthof the inclined bearing face 22 and substantially perpendicular to thelatter. Hence, if the flanks 22 are inclined by an angle α with respectto the plane of the upper face 10 of the strip, the bearing forces F aresubstantially inclined by the complementary angle α1.

It is to be noted that, as shown in the two schemes of FIG. 2, it ispossible to vary the inclination angle α of the flanks 22, 23 withrespect to the mean plane of the strip and, hence, the complementaryinclination angle α1, α′1 of the bearing forces F, F′. However, theinclination angle α1, α′1 must not exceed 45° so as to avoid a risk ofcleaving of the concrete by wedge effect.

Taking into account that the locks 2 are rectilinear and extend almostover the whole width I of the strip 1, each of said locks 2 exerts onthe concrete, through its front face 22, bearing forces directedfollowing a mean plane P inclined by the angle α1 with respect to thewide face 10 of the bar 1.

Likewise, each of the locks 2′ of the lower face 10′ of the strip 1exerts on the concrete, through its front face 22′, bearing forces thatare directed following a mean plane P′ inclined by an angle α′1 withrespect to the lower face 10′ of the strip 1.

Hence, when a reinforcing bar in the form of a strip 1 is subjected to atensile force T, all the parallel grooves 2, 2′ formed on the two widefaces 10, 10′, respectively, of this strip 1, exert on the coatingconcrete bearing forces substantially directed following two series ofparallel planes P, P′ symmetrically inclined with respect to the twofaces 10, 10′ of the strip 1.

Moreover, due to the trapezoidal profile of the locks 2 and the grooves3, the inclined flanks 22, 22′ of the grooves 2, 2′ that extend overalmost the whole width of the strip, have a substantially constantheight, such that the forces applied by each by each lock on theconcrete, when the bar is subjected to a tension, are uniformlydistributed over the whole length of the lock, i.e. over the whole widthof the bar 1.

Furthermore, as each bar has, in cross-section with respect to its axis,a rectangular profile of small thickness with respect to its width, theprojection of the locks in the longitudinal direction of the tensileforce, which corresponds to the stress transmitted by the bar to theconcrete, may extend over at least 75% of the perimeter of the bar,calculated from the nominal cross-section of the latter. It resultstherefrom a lesser risk of shearing of the junction.

Besides, the longitudinal spacing of the mean planes P, P′ of thebearing forces on the concrete corresponds, on each face 10, 10′ of thestrip, to the reduced pitch c of spacing of the elongated locks 2, 2′,which, as indicated above, is smaller than half the width of the strip1. Therefore, the stop stresses that are exerted along two directionssymmetrically inclined on either sides of the mean plane of the strip,along two series of parallel planes P, P′, not much separated from eachother, are hence distributed in a substantially uniform way over thewhole width and the whole length of the bar 1.

This uniform distribution of the stop stresses in all the concretesheath surrounding the bar favours, from a limit tensile force, theprogressive formation of a set of microcracks, the opening of whichremains acceptable and, in case of increase of the tensile force, thenumber of microcracks increases, which allows to avoid theirlocalization into macrocracks of harmful opening.

This uniformization, along a reinforcing bar in tension, of thedistribution of the bearing forces on the concrete hence allows to alsodistribute, over a greater length, the tensioning of the concrete, andhence the risk of cracking. Therefore, when the tensile forcetransmitted to the concrete exceeds the strength of the latter, thisforce may be distributed over a certain length of the bar, by formingprogressively multiple cracks of small width, allowing to avoid anexcessive widening of a localized crack.

Besides, as mentioned above, the locks 2′ of the lower face 10′ of thebar are shifted by a half-pitch with respect to the locks 2 of the upperface 10 and are hence placed substantially opposite to the grooves 3between these latter. It results therefrom that the cross-section ofmetal on which is applied the tensile force T remains substantiallyconstant over the whole length of the strip, which hence participates intotality to the strength whereas the resistance of a conventionalcircular cross-section reinforcing bar has to be calculated only as afunction of its nominal diameter, without taking into account the volumeof metal corresponding to the anchoring portions.

It is to be further noted that the production of elongated locks andgrooves extending over the whole width of the strip allows to keep allthe advantages offered by the use of a flat strip as a reinforcing bar.

In particular, due to the fact that the perimeter of a rectangularcross-section flat bar corresponds to about 1.5 times the circumferenceof a round bar of same cross-section, the use, as reinforcements, offlat bars provided, according to the invention, with elongated locksthat are close to each other, allows to increase the adherence link onthe embossed faces 21 of the locks 2 and the bottoms 31 of the grooves3.

Moreover, it is known that, in a round bar provided with projectingcircular locks, the sudden variations of cross-section of the materialmay lead to a certain brittleness at bending of the bar. On the otherhand, the use of reinforcing bars according to the invention, includinga great number of nearly spaced apart and small height locks, allows toreduce this risk of brittleness at bending of the bar, for example toform anchoring hooks at the ends or to adapt the profile of the bar tothe shape of the component or to the distribution of stresses in theconcrete component.

However, as the locks 2 and the grooves 3 extend almost over the wholewidth I of the strip, their ends risk to form sharp angles harmful forthe handling of the bar and able to facilitate a cracking of theconcrete at the tensioning of the bar.

That is why, as shown in the drawings, the locks 2 and the grooves 3extend transversally over only a width that is a little smaller thanthat of the flat strip 1, so as to leave, along each of the two lateraledges of the latter, a smooth flat 12 having a small width, for exampleof the order of 0.2 e, e being the thickness of the strip at each of itssides 11.

In the embodiment of FIGS. 1 and 2, the elongated locks 2, 2′, formed onthe two faces 10, 10′, respectively, of the strip, and separated fromeach other by the grooves 3, 3′, are directed perpendicular to thelongitudinal axis x′, x of the bar. It is however more advantageous, inanother embodiment of the invention, shown in perspective view in FIG.3, that the elongated locks 2, 2′ of the two faces 10, 10′ of the stripare inclined by a certain angle 13 with respect to the longitudinal axisx′, x of the strip 1.

It is hence the same for the planes P, P′ in which are located, asabove, the bearing forces exerted by all the locks 2, 2′ on the coatingconcrete.

That way, as shown in FIGS. 3 and 4, each of the two faces 10, 10′ ofthe bar 1 has, in a direction perpendicular to the longitudinal tensileforce T, an alternation of projecting portions and of recessed portionscorresponding to several inclined locks 2 a, 2 b, 2 c, whose bearingfaces 22 cross the cross-sectional plane. It results therefrom a betteruniformization, along the longitudinal axis x′ x, of the bearing forcesexerted on the concrete by the two grooved faces 10, 10′ of the bar 1,when the latter is subjected to a longitudinal tensile force.

The inclination angle β of the locks may be the same on the two faces10, 10′, which are then provided with parallel locks 2, 2′, which, asabove, may be shifted by a half-pitch, so that each lock on a facecorresponds to a groove on the other face.

However, in another embodiment even more advantageous and shown in topview in FIG. 5, the two series of locks formed on the two wide faces 10,10′, respectively, of the strip are symmetrically inclined by angle β onthe upper face 10 and by the opposite angle 13′ on the lower face 10′.Therefore, the possible effects of lateral shift are compensated and thestrip 1 remains better centred on the longitudinal axis x′, x ofapplication of the tensile force T. Moreover, as each of the two faces10, 10′ includes, in cross-section, an alternation of projectingportions 2 and recessed portions 2′, shifted by a small height withrespect to the thickness of the strip, the whole cross-section of thelatter remains substantially constant over the whole length thereof.

As above, the inclined locks 2, 2′ and the grooves 3, 3′ are stopped ata small distance from the lateral edges of the strip 1, so as to form,along each of the sides and on each face 10, 10′ of the strip 1, asmooth flat 12, 12′ having a small width, of the order of 0.2 e.

Besides, as shown in FIG. 4, on each of the wide faces 10, 10′, theembossed faces 21, 21′ of the locks 2, 2′ and the bottoms 31, 31′ of thegrooves 3, 3′ are located in parallel planes, respectively, extending oneither side of a mean plane of the strip and in which are placed thesmooth flats 12, 12′.

The invention also covers an original method of producing suchcorrugated flat bars from a commercial wire rod or, more generally, of acircular cross-section smooth bar.

In this method, as schematically shown in FIG. 10, such a round bar 4may be firstly subjected to a first rolling pass between two cylinders41 rotating about horizontal axes 40, so to provide it with the desiredthickness e, then to a second rolling pass between two cylinders 42rotating about vertical axes, to adjust the width I thereof. It is henceobtained a rectangular cross-section flat strip 1, which is thensubjected to a third rolling pass between two opposite rolls 5, 5′rotating about horizontal axes 50, 50′ parallel to the wide faces 10,10′ and each provided on its periphery with an alternation of recesses51, 51′ intended to form the locks 2, 2′ and with teeth 52, 52′ intendedto form the grooves 3, 3′, as schematically shown in FIG. 11, which is adetail sectional view according to a plane I,I passing by the axes 50,50′ of the rolls 5, 5′.

Preferably, the recesses 51 and the teeth 52 formed on the periphery ofeach of the rolls 5, 5′ do not extend over the whole width of theselatter, so as to leave, at their ends, smooth portions 53, 53′ for theformation of the flats 12, 12′ along the lateral edges of each of thetwo faces 10, 10′ of the strip 1.

Moreover, to facilitate the putting in place of the concrete in thegrooves 3 and to avoid sharp angles at the ends of the locks 2, therecesses 51 and the teeth 52 formed at the periphery of the rollingcylinders 5, 5′ have a trapezoidal section, both in lengthwise andcrosswise, so that, on each of the faces 10, 10′ of the strip 1, thelocks 2 are connected, at each end, to the corresponding flat 12, by aninclined face 24, just as the grooves 3 that are terminated, at eachend, by an inclined face 34 (FIG. 3).

Such corrugated reinforcing bars provided, on their wide faces, withparallel locks and grooves with a trapezoidal cross-profile, allow tokeep all the advantages offered by the use of flat reinforcing bars forthe making of a reinforcing cage, for example as described in thedocument FR-A-2 814 480.

FIG. 8, for example, is a schematic, longitudinal sectional, detail viewof a concrete component 6 such as a beam or a slab subjected to flexionforces, having two parallel facings, respectively a face 61 in tensionunder the effect of the forces applied and a compressed face 62, andwherein is embedded a reinforcing cage 7 including two webs oflongitudinal bars 71, 72 crossing transverse bars 71′, 72′, which extendat a small distance of coating of the facings 61, 62, respectively, andare connected to stirrups 73. As described in the document FR-A-2 814480, the longitudinal and transverse bars consist advantageously in flatstrips, as well as transverse stirrups that may be consisted of acorrugated strip alternately welded, by its tops, to the two webs ofbars, or of a series of flat tabs shaped so as to form, at their ends,two planar faces for the welding to the bars of the two webs,respectively.

According to the invention, the longitudinal bars 71 extending along theface 61 in tension consist in corrugated flat strips of theabove-described type, comprising, on each wide face, a series ofparallel anchoring locks separated by grooves. However, the transverseflat reinforcing bars 71′ as well as the stirrups in the form ofcorrugated strips 73 can also be easily welded to the planar embossedfaces 21 of the elongated locks 2, due to the trapezoidal profile andthe small width of these latter.

Moreover, the arrangement of FIGS. 3 and 4, including, on each wideface, a series of parallel locks, inclined by a same angle with respectto the longitudinal axis x′ x of the bar 1, allows to apply and weldeach transverse bar 71′ to the embossed faces 21 of several neighbourlocks, and it is the same for the stirrups 73, at the top of thecorrugations.

Of course, the invention is not limited to the embodiments describedabove by way of simple examples but also covers all the variants usingequivalent means and remaining in the same protective framework.

In particular, if it is advantageous that the locks 2, 2′ are spacedapart by a constant pitch c, along each face 10, 10′ of a bar 1, itwould be possible, in certain cases, to adjust the distribution of therecesses 51 and the teeth 52 over the periphery of the rolling cylinders5, 5′, to vary periodically the spacing of the anchoring locks. Forexample, it could be made, on each face 10, 10′ of the strip 1, analternation of blocking areas provided with locks and of areas leftsmooth, as described in detail in the document WO 2010/067023 A1, so asto distribute the risk of cracking over le length of the component, byreducing the opening of the cracks under a certain load.

On the other hand, the elongated locks 2, 2′ formed on the two faces ofthe strip, do not necessarily extend in straight line between the twosides 11 a, 11 b of the strip 1.

FIG. 9, for example, shows two variants of the invention. The upperportion shows, in top view, a flat bar 1 provided, on its upper face 10,with anchoring locks 2 in the form of imbricated chevrons, centred onthe longitudinal axis x′, x of the strip. The opposite face 10′ is alsoprovided with imbricated-chevron locks that may be rotated in the samedirection or in the opposite direction, so as to better resist toalternated tensile forces.

The lower portion of FIG. 9 shows another variant in which the locks 2a, 2 b are arranged in two lines that extend only over half the width ofthe strip 1 and are alternately inclined toward the right or toward theleft of the longitudinal axis x′, x.

Moreover, it is more advantageous that the flanks of the locks arerectilinear, so that the bearing forces are exerted following asuccession of parallel planes, but corrugated locks could also be made.

Furthermore, if it is preferable to subject the round bar to twosuccessive rolling passes, as shown in FIG. 10, to adjust precisely thethickness and the width of the flat strip, it is however not necessarythat the latter has a strictly rectangular cross-section. Indeed, in asimpler embodiment, it would be possible to subject the round bar to asingle rolling pass to obtain an oblong cross-section strip, as shown inFIG. 12, wherein such a strip can also be provided with elongated lockson each of its wide faces.

Finally, the grooves of the wide faces of the strip could be eliminatedat certain places and over a small length, for example for marking thebar.

1. A reinforcing bar with improved adherence for a reinforced concretecomponent, consisting in of a metal section (1) extending in alongitudinal direction, having the form of a flattened strip ofsubstantially rectangular cross-section, with two opposite wide faces(10, 10′) extending between two lateral sides (11, 11′) and including aplurality of projecting anchoring portions which are longitudinallyseparated from each other and bearing on the concrete in a directionopposite to a tensile force applied to the bar (1), characterized inthat each of the two wide faces (10, 10′) of the strip is provided witha series of anchoring portions in the form of elongated locks (2, 24)separated from each other by hollow portions (3, 3′) in the form ofgrooves and extending transversally over the whole width of the strip(1), substantially up to the lateral sides (11, 11′) thereof, and eachof said elongated locks (2) extends in projection over a small height,not exceeding a quarter of the thickness of the strip (1), and has, incross-section, a substantially trapezoidal profile, with an embossedface (21) of small width with respect to its length and two inclinedflanks (22, 23) for connection with the elongated bottom (31, 31′) ofthe adjacent grooves (3, 3′) that constitute, for each lock (2), twoinclined faces (22, 23) that bear, each in one direction, on the coatingconcrete, said inclined faces (22, 23) each having an elongated shapeextending between the two sides of the strip (1), so as to distributethe bearing forces over all the width thereof.
 2. The reinforcing baraccording to claim 1, characterized in that, on each face (10, 10′) ofthe strip (1), the elongated locks (2, 2′) are spaced apart from eachother by a constant pitch (c) that do not exceed half the width (1) ofthe strip (1).
 3. The reinforcing bar according to claim 1,characterized in that, on each face (10, 10′) of the strip (1), theembossed faces (21, 21′) of the elongated locks (2, 2′) have a widthlower than half the width (1) of the strip (1).
 4. The reinforcing baraccording to claim 1, characterized in that the elongated locks (2, 2′)extend transversally in directions inclined by a non-zero angle withrespect to a longitudinal axis of each face (10, 10′) of the strip (1).5. The reinforcing bar according to claim 4, characterized in that theelongated locks (2, 2′) formed on the two faces (10, 10′), respectively,of the strip (1) are symmetrically inclined, in opposite directions,with respect to the longitudinal axis X′, X of the strip (1).
 6. Thereinforcing bar according to claim 4, characterized in that, on eachface (10, 10′) of the strip (1), the elongated locks (2, 2′) areparallel and inclined by an angle β comprised between 35° and 75°. 7.The reinforcing bar according to claim 3, characterized in that theanchoring locks (2, 2′) formed on each wide face (10, 10′) of the strip(1) have the shape of imbricated V-shaped chevrons, with two rectilinearportions symmetrically inclined on either side of a longitudinal axis(X′, X) of the strip (1).
 8. The reinforcing bar according to claim 4,characterized in that the anchoring locks (2, 2′) formed on each wideface (10, 10′) of the strip (1) have a corrugated shape, symmetricalwith respect to the longitudinal axis (X′, X) of the strip (1).
 9. Thereinforcing bar according to claim 1, characterized in that, on eachwide face (10, 10′) of the strip (1), the elongated anchoring locks (2,2′) extend up to a small distance from each of the lateral edges (11 a,11 b) of the strip (1), so as to leave a smooth flat (12) of small widthalong each of said edges (11, 11′).
 10. The reinforcing bar according toclaim 9, characterized in that the flats (12) formed along the twolateral edges (11, 11′), respectively, of the strip (1), on each of widefaces (10, 10′) thereof, have a width of the order of 0.2 e, e being theaverage thickness of the strip.
 11. The reinforcing bar according toclaim 9, characterized in that, on each wide face (10, 10′) of the strip(1), the embossed faces (21) of the locks (2) and the bottoms (31) ofthe grooves (3) are located in the two parallel planes, respectively,extending on either side of a mean plane Q of the wide face (10), inwhich are placed the two flats (12 a, 12 b) extending along the twolateral edges (11 a, 11 b), respectively, of the strip (1).
 12. Thereinforcing bar according to claim 11, characterized in that the twoplanes in which are located the embossed faces (21) of the locks (2) andthe bottoms (31) of the grooves (3), respectively, are spaced apart by aheight h that can be from 0.08 e to 0.24 e, e being the averagethickness of the strip (1).
 13. The reinforcing bar according to claim1, characterized in that the connection flanks (22, 23) between theembossed faces (21) of the locks and the bottom (31) of thecorresponding grooves (3) are inclined by an angle α of at least 45°,with respect to a plane in which said embossed faces (21) are placed.14. The reinforcing bar according to claim 1, characterized in that theanchoring locks (2) are longitudinally spaced by a pitch (c) comprisedbetween one and three times the average thickness e of the strip (1).15. A reinforcing cage (7) for a reinforced concrete component (6)including two webs of reinforcing bars connected by stirrups andextending at a small distance of coating from two spaced-apart facings(61, 62), respectively, of the component (6), characterized in that atleast one of the two webs of the cage consist in bars (71) with improvedadherence according to claim 1, and in that the stirrups are formed offlat metal strips (73), alternately welded on the embossed faces (21) ofthe anchoring locks (2) of said improved-bond bars (71).
 16. A method ofproducing a reinforcing bar according to claim 1, characterized in thatit is firstly made a metal bar (1) in the form of a flattened strip withtwo opposite wide faces (10, 10′) and centred on a longitudinal axis (x′x), and in that said strip (1) is subjected to a rolling pass betweentwo cylinders (5, 5′) rotating about axes (50, 50′) parallel to eachother and orthogonal to the longitudinal axis (x′ x) of the strip (1),said cylinders (5, 5′) being provided, over their periphery, withspaced-apart recesses (51), for the formation, by rolling, of elongatedlocks (2) separated by parallel grooves (3), on each of the two widefaces (10, 10′) of the strip (1).
 17. The method according to claim 16,characterized in that the two rolling cylinders (5, 5′) are eachprovided, over their periphery, with an alternation of recesses (51) andteeth (52) intended to form the locks (2) and the grooves (3),respectively, on each of the wide faces (10, 10′) of the strip (1) andextending between two smooth portions (53) for the formation of twoflats (12) along the two lateral sides (11 a, 11 b) of the strip (1).18. The method according to claim 16, characterized in that the recesses(51) for the formation of the locks (2) are regularly spaced apart alongthe periphery of each of the rolling cylinders (5, 5′).
 19. The methodaccording to claim 16, characterized in that the recesses (51) aredistributed along the periphery of each of the rolling cylinders (5, 5′)so as to periodically vary the spacing of the locks (2) obtained on eachwide face (10, 10′) of the strip (1).
 20. The reinforcing bar accordingto claim 2, characterized in that, on each face (10, 10′) of the strip(1), the embossed faces (21, 21′) of the elongated locks (2, 2′) have awidth lower than half the width (1) of the strip (1).